The applicant has developed a novel approach to drug delivery which is described in full in international patent applications PCT/EP02/10394 and PCT/EP03/07859. The content of both these applications are included by reference.
In international patent application PCT/EP02/10394 and referring in particular to FIG. 16 of PCT/EP02/10394, there is illustrated a delivery or actuator device fitted with a disposable assembly, the disposable assembly being referred to as a drug cassette. The disposable assembly comprises a casing having a central aperture or chamber in which is mounted an injectate comprising a pioneer projectile and a formulate or drug. The pioneer projectile may be inert or a pharmaceutical product. The pioneer projectile and drug may be separate or a single unit, for example, in the form of a single rod or pin or needle type structure; the pioneer projectile being the sharp or piercing end of the rod.
A large headed ejector pin (also referred to as a drive pin) comprising a flat head and an elongate body is positioned over the injectate so that when the ejector pin is contacted, in use, by a striker or hammer, the injectate is pushed along the central aperture or chamber and out into the patient. A resilient member, such as a rubber block, urges the ejector pin back a little after injection.
The disposable assembly is loaded into the actuating device by, for example, screwing it into the lowermost end of the inner housing.
The disposable assembly is shaped such that when it is in contact with the skin it pre-tensions the skin to actuation. This ensures that the injectate will penetrate the skin rather than just stretch the skin.
Where the ejector pin or drive pin is used with a needle or lancet the non skin contacting end of the needle or lancet may constitute the pin and typically, though not essentially, a drive head will be provided thereon.
The ejector pin is designed to push the injectate beyond the end of the actuator device by up to (say) 2.5 mm. This means that the end of the ejector pin (which preferably has the same profile and diameter as the end of the pioneer projectile) might just penetrate the skin to ensure that the injectate has been fully administered into the skin.
When the actuator device is actuated the striker or hammer travels along the striker guide until it contacts the head of the ejector pin with a force that causes the injectate to pierce the skin. The ejector pin continues to push the formulation into the patient to the required depth, which is determined by the length of the injectate and the extent to which it is pushed by the ejector pin. A rubber stop is squashed by the ejector pin head during delivery of the injectate but the elastic properties of the rubber stop enable the tip of the ejector pin to be withdrawn into the disposable component of the device.
The later filed application, PCT/EP03/07859, describes in more detail a drug delivery device suitable for delivering drugs using a pioneer projectile instead of a traditional needle to pierce the skin. However, the device may also be used to cause a traditional capillary needle or needle lancet to pierce the skin, as described with reference to FIG. 4 therein.